Method of producing photographic emulsions



Patented May 16, 1939 i 2,158,219 METHOD or PRODUCING rno'roG EMULSIONS 'nrc Bruno Claus, Halle-on-the-Saale, Germany No Drawing. Application January 15, 1937, Se- In Germany January 20.

q 5 Claims; (cl.- 95-4) My invention relates-to photographic emul rial No. 120,783. 19se .sions and more especiall-yto the production of peptisation emulsions, in which asedimentof silver halide precipitated from a solution and v sufficiently freed from the adhering solution; for 1 instance by decanting and warning, is mixed with a binder, 'for instance with a-gelatine solution and allowed to age.

The production of such peptisation emulsions offers great advantages, since-the time-consum ing and little reliable washing process. can be dispensed with and since these emulsions possess a higher sensitivity than emulsions of the same order of grain sizeproducedaccording to bustomary methods. Preferably, when emulsifying the silver halide sediment subsequently mixed.-

with the binder, so-called peptisation agents,'for instance ammonia, are added, but hitherto a comparatively too large proportion of such agent such as ammonia was required. r

I have now found that in the emulsificati'onpf the silver halide sediment in a gelatine solution as well as in the ageing'of the mixture of silver halide sedimentvand gelatine the absolute quantity of the peptisation agent such as a solution of ammonia is unimportant, the concentration of the agent such as ammonia being alone decisive. Consequently it appears inadvisable to carry through emulsiflcation and ageing in the whole of the quantity of gelatine' solution, since this would only require an unnecessarily large quantity of ammonia injurious to peptisation emulsions to obtain the ammonia concentration-which is necessary and most favorable for emulsification and ageing. I have found that it .is far better to emulsify and also to age the light-sensitive sediment at first only in a small part, less than one half or one fourth or one sixth, and in some case in as little as one tenth or one thirtieth or 40 one fiftieth of the total emulsifying liquid, since I am thus enabled to effect a great saving in ammonia.

Therefore, in accordance with the present in- 4 vention, I mix the silver halide sediment, which 5 has beensufiiciently freed solution, with less thanpne third and preferably less than one fifth or one tenth of the total quantity of the emulsifying solution. (aqueous 50 gelatine solution) and allow it to age therein,

while adding, gradually or as a whole, the larger part of the emulsifying solution only after emulsiflcation of the sediment in the first part and after it has already been allowed to more or less age therein.

from the adhering Before adding the balance of theeinulsiflcation solution, which may be addedin instalments, I prefer expelling the ammonia, by evaporation or otherwise, sufliciently -to ensure stability of the photographic emulsions and .for'this purpose I heatthe first mixture of the sediment and the smaller part of the. emulsifying solution under continuous stirring in a'low layer, air being paused to sweep the surface of theliquid or to in the liquid etc., in order to facilitate the escape of the ammonia.

In the operation of my invention 1 may for instance proceed as'follows: Into asolution of potassium bromide and w potassium iodide, wherein'the proportion of KBr to KJ is 25:1 and which contains 0.5% gelatine, a 10% silver nitrate solution is entered under continuous stirring in such manner that a'slightexcess of bromine, for instance 1%, remains over,

so'that the proportion of silver nitrate solution to potassium halide solution is about 100273. After the silver halide has settled down as a sediment, the supernatant liquid is decanted and the silver halide sediment washed.- .Now one sixth 'of the 10% gelatine solution heated'to 50 0.

used in ,the preparation of the emulsion' is mixed. with so much of a 25% ammonia solution that the gelatine solution contains 5% ammonia. This solution is-now poured under continuous stirring so overthe silver-halide sediment. The: mixture iskept thirty minutes at 50 C. andis then poured in a shallow tray, the height of the liquid being preferably not above 5 cms. The mixture is now I kept another hour at about 50 C.,- under con'- tinuous stirring, whereby it is substantially freed from the ammonia. Now ,the remaining five sixths of the gelatine solution, to which no ammonia had been added, are mixed with the preliminary emulsion, so that this concentrated emulsion is now reduced to the normal concen-. tration of about 7%. This normal emulsion may. now still be allowed to age until it has reached the maximum sensitivity and may then be poured.

Obviously the proportions andk temperatures 4 mentioned-in this example may be varied withinwide limits, provided only that thesilverhalidefl sediment, precipitated from a silver solution and sufflciently freed from the adhering solution, is v mixed. first with a comparatively small partiof the whole of the emulsiflcation liquid, the emulsifying agent such as ammonia being added to themixture and the sediment is emulsified and if desired, also allowed toage in this part, while the rest of the emulsifying solution is added only 5 I departing fromthe invention or sacrificing the advantages thereof.

' I claim:

1. In the process of producing photographic emulsions the steps of emulsifying a wet silver halide sediment in less than one third of the.

total quantity of the water and of the gelatine required to produce a photographic emulsion, ready to be poured, which contains said silver halide, allowing the silver halide to age therein in the presence of an aging agent and thereafter mixing the ripened product with the rest of the water and gelatine.

2. The process of claim 1, in which, after the silver. halide sediment has been emulsified and aged in the presence of an aging agent, said agent is rendered at least partially inactive.

3, The process of claim 1, in which, after the silver halide sediment has been emulsified and gelatine."

aged in the presence of ammonia in a concentration in which ammonia acts as an emulsifying and aging agent, the main part of the ammonia is removed by evaporation.

4. The process of claim '1, in which, after anotherpart of the required quantity of water and 'gelatinehas been added, the whole is allowed to age further.

5. The process which comprises precipitating a silver salt solution with an alkali bromide solution in the presence of a small quantity of an alkali iodide and of gelatine, allowing the silver halide produced in the reaction to settle, decanting the supematant'liquid, washing the sediment, emulsifying the silver halide sediment in less than one third of the total quantity of the water and of the gelatine required to produce a photographic emulsion ready to be poured, which contains said silver halide, allowing the silver halide to age therein in the presence of an emulsify-v ing, and aging agent and thereafter mixing the ripened product with the rest of the water and ammo CLAUS. 

